1. Two characteristic properties of the specific high-affinity steroid-binding proteins or receptors, their ability to bind to DNA–cellulose and their relatively acidic isoelectric point, have been exploited as a means of purification. These two fundamental properties distinguish the receptors from the steroid-binding proteins in serum and the non-specific low-affinity steroid-binding proteins in hormone-responsive cells. 2. A significant degree of purification of both cytoplasmic and nuclear steroid–receptor complexes can be achieved with practical facility by these procedures. The purity of the receptor complexes is sufficient to enable studies on their possible control of metabolic processes to be investigated in the future. 3. After extensive purification the physicochemical properties of the cytoplasmic androgen–receptor complex, such as sedimentation coefficient, were unchanged. Further, the purified complex fully retained at least one of its fundamental physiological properties, namely the ability to transfer 5α-dihydrotestosterone (17β-hydroxy-5α-androstan-3-one) into chromatin in vitro. 4. The methods may also be employed for studying the changes in the structure and properties of the receptor complexes that are an essential prerequisite for the transfer of cytoplasmic receptor complexes into nuclear chromatin. The temperature-dependence of the binding of androgen–receptor complexes into chromatin is essentially due to a major change in cytoplasmic receptor complex before its attachment to nuclear chromatin. 5. The resolution of these analytical procedures was sufficient to enable a critical comparison of the receptor proteins from different male accessory glands to be undertaken. From these studies, no substantial evidence in support of the tissue specificity of androgen receptors could be established; rather the receptors from different androgen-dependent glands were remarkably similar in physicochemical properties. 6. Although the methods were initially developed for the partial purification of androgen–receptor complexes, they are equally suitable for the prompt and extensive purification of oestrogen–receptor and progesterone–receptor complexes.
The Hsp56 component of steroid receptor complexes binds to immobilized FK506 and shows homology to FKBP-12 and FKBP-13.
